Multitap resistor and method of making same



Oct. 24, 1950 J, MUCHER MULTITAP RESISTOR AND METHOD OF MAKING SAME Filed May 15, 1948 7%! gr a4 25 2502 mm M M flTTUR/VEYS Patented Get. 24, 1950 MULTITAP RESISTOR AND METHOD OF MAKING SAME George J. Muchcr, Brooklyn, N. Y., assignor to Clarostat Mfg. 00., Inc., Brooklyn, N. Y., a corporation of New York Application May 13, 1948, Serial N 0. 26,764

This invention relates to a functionally and structurally improved multitap resistor.

In the construction of wire wound resistors having a number of tap-s arranged so that several resistance values may be derived from a common unit, it is conventional to afiix the terminal posts to the windings by means of sleeves which are crimped about the Winding. Under present practice a resistance is wound with a continuous length of wire of constant resistance value and resistance legs of various ohmages are derived by suitably spacing the terminal sleeves. Where it is necessary to have a low resistance portion, the terminal sleeves must necessarily be close together. Manufacturers of electrical equipment in which resistorsare used allowa maximum departure from the specified resistance value of only 10 per cent. Where specifications call for a low resistance section, the length of winding between the terminals will be small. Evena slight shift or misplacement of one of the terminals during construction will result in a resistance value which is not within the permitted tolerance, and the unit may be rejected by the purchaser. For that reason manufacturers of multitap wirewound resistors have established minimum spacings between adjacent taps, and at times therefore a customers specification cannot be met be cause of this small spacing.

In a resistor constructed according to the present invention. there is employed instead of a continuous winding of uniform resistance wire, a series of individual wire-wound resistance elements, each element having a wire size which provides a specified resistance between successive terminal taps, while also affording a spacing between the taps of a resistance leg, such that substantially less than the permitted ten per cent variation from the specified resistance will occur.

For example, where in the old construction the resistance value of a section might require only A; of an inch of windinga length far too short under present practices because of the impossibility of maintaining the standard tolerance-the same value in a resistor made pursuant to the present invention might comprise a winding having a length of more than an inch. In such a length, a slight misalignment of the terminal tap or sleeve will result in only a very small change of resistance value.

Other features of the present invention reside in a novel core construction which makes it convenient to bring the terminal leads to a connection block or base at one end of the resistor, or optionally to take the terminal leads radially 5 Claims (01. 20171) 2 from the unit, andmeans whereb 'one or more separate and distinct, resistance legs may be included on a core having a multitap resistance winding without increasing the overall length of the unit to the extent necessary in resistors made pursuant to present practice.

It is another object of the invention to provide a resistance unit whereby a plurality of individual wire-wound resistors are arranged helically about a common core and suitably provided with terminal taps.

It is yet another object of the invention to provide a multitap resistance unit embodying a resistance element wound helicall upon a core, said core having means for supporting a plurality of terminal connection means at any position lengthwise 0f the core, whereb connection may be made with said resistance element at any point along the length thereof.

It is a further object of the invention to provide an improved means of mounting the terminal taps of a multitap resistance.

It is also an object of the invention to provide a multitap resistor having means for mounting the terminal taps for axial, or radial extension relative to the core of the unit.

An additional object is that of providing a unit of this type which will include relatively few parts each individually simple in design and rugged in construction; such parts being capable of manufacture b quantity production methods and when assembled providing a unit which will have a long effective life.

With these and other objects in mind, reference is had to the attached sheet of drawings illustrating one practical embodiment of the invention and in which:

Fig. 1 is a vertical elevation, partly in section, of a resistor constructed pursuant to the present invention;

Fig. 2 is a sectional plan section taken on lines 2-2 of Fig. 1;

Fig. 3 is a partial plan section taken on lines 33 of Fig. 1;

Fig. 4 is an exploded perspective of a portion of the resistor core and of the tap terminals used in connection therewith; and

Fig. 5 represents a typical inultitap resistance specification in the fulfillment of which resistors manufactured pursuant to the present invention are particularly well suited; such view also showing in a somewhat schematic manner one circuit arrangement which may be incorporated in accordance with the present teachings.

Referring initially toFig. 4, a cylindrical core II] is formed with a plurality of axially extending slots II which have a narrow entrance I2 and enlarged channel or passage I3. Said slots may each therefore conveniently be in the form of an inverted T. The core is of insulation material, and may be circular or polygonal in crosssection. Where the resistor is to have a highwattage rating, the core is most preferably of inorganic material such as molded or extruded ceramic, but other insulation materials appropriate to the characteristics of the ultimate resistor may be utilized.

The slots II are intended to receive striplike connection terminals I4, either having integral heads I or heads I6 afiixed thereto. Said heads are to make contact with the resistor winding as later described, and therefore may be substantially cylindrical for crimping about the resistance winding, as shown in Fig. 1. The selection of single or double-banded head depends 'upon the conditions later described. The width of the respective terminal strips I4 is suitable for slidable insertion within the passages I3, and said strips may be flexed or arched (see Fig. 1) for frictional engagement with the facing walls of the passage. The connection heads I5 and I6 are provided with neck portions I! to slidably enter the entrances I2 to permit the strips I4 and their relatively wide heads to he slid along the length of any groove II. The head of any strip may then be brought to any suitable position intermediate the ends of the core.

Fig. 5 represents a typical specification for a completed resistor. It will be noted that the first resistance, between the terminals A and B, is an independent unit, whereas each of the terminals D, E, F, and G is common to two resistance windings. Therefore the terminals A, B, C, and H, employ the single head I5, whereas the terminals D, E, F, and G advantageously use the branched or double-banded heads I6. In the latter heads, the two branches Mia and IE2) are separated by a gap IBc provided for the convenient insertion of a cutting tool to remove the excess length of winding after the respective branches have been crimped thereabout, as later described.

The respective resistance elements I8 advantageously comprise resistance wire wound on a flexible core I9, which is preferably a strand of fiberglass or similar inorganic insulation material. In manufacturing practice the resistance elements are wound as a continuous length which may be of the order 500 or 750 lineal feet depending upon the footage of the cord reel and the wire reel. It is presumed that the manufacturer will have in stock reels of wire-wound strands, each strand representing a specific resistance value per unit of lineal measurement.

When a specified resistor is to be manufactured the engineer will ascertain the required ohmage and wattage between the various taps from the specification and from his knowledge of the resistances in stock and the lineal resistance values thereof, will calculate the length of a selected resistance element necessary to comply with the specification. Obviously, a specified resistance may be derived, for example, from an inch of one resistance material or a yard of another; the engineer, knowing the outside diameter and length of the core I0 and the spacing between slots, and using a standardized pitch of winding, such as eight turns to the inch, selects his resistance material accordingly.

For purpose of illustration, assume that each of the several resistance legs specified in Fig. 5 requires a different weight of resistance wire. The factor which will determine the selection of the appropriate resistance material is, of course, the total length of material required to meet the specifications. I prefer to have each element extend for at least one half of a complete turn about the core I0, because, as has been stated, the tolerance limitations are best met when there is a substantial length of resistance material between the end terminals or connection heads thereof.

After the engineer has selected the necessary resistance components, he will prepare a winding specification for the manufacturing department, said specification noting how many turns or fractions of a turn of each grade of resistance material are to be wound on the core. The first manufacturing step is to insert the terminal head A in a slot II and crimp the head about the end of the resistance material so as to make good electrical contact therewith. The specified length is wound upon the core and th resistance wire clipped within the second terminal head B, which had been previously inserted into the appropriate slot. The excess of resistance material is clipped to complete the independent resistance leg between the terminals A and B. A second resistance winding, according to the specification, is begun commencing with the terminal 0, which has been placed in the next appropriate slot. The second resistance leg terminates at one branch of the double-head connector D and is clipped thereat. The third leg commences at the other branch of terminal D, and terminates at the appropriately positioned succeeding terminal head; and the remainder of the core is wound appropriately.

In order to insure that the successive turns remain in insulated spaced relationship, a spacer winding 20 of fiberglass cord may be afiixed to the end terminal A and continuously wound to separate each of the convolutions of the resistance elements with a resilient insulation material. The end of said insulation winding may be clipped to the end terminal H or otherwise secured.

Obviously other methods of maintaining a spaced relationship, such as forming the outer surface of the core ID with a continuous shallow helical groove at the desired pitch may be employed.

The thus-wound core may then be operated on to cut the protruding ends of the respective strips I4 to a common length. It has been found expedient to offset the ends of the respective strips with a short right-angled jog 22 so as to prevent accidental movement of a strip I4 within the slot during the later fabrication of the completed device.

It will be understood that the eight-slotted core III is illustrative only, and that a specified resistor may not require that all of the slots be utilized. The end-connected unit shown in Fig. 1 is also a specific form which may not always be required.

It may be desired, for example, to have radially extending lead wires connected to the various terminal heads. The respective heads may thus be mounted on strips I4 having a length sufficient only to frictionally grip the walls of a. slot II, and Wires or other leads may be soldered or attached directly to the heads instead of to the base-projecting strips I4 in the Fig. 1 embodiment.

Such lead wires as are connected directly to the heads may be brought out through the side wall openings 23 of the ventilated housing or cover 24 within which the wound unit is placed.

Fig. 1 illustrates one method of enclosing the wound core in the ventilated housing 24. A plate 25 of suitable insulating material is suitably punched to accommodate the ends of the strips l4. Said plate has ears or extensions '26 to which a cup 21 of metal or other suitable material may be fastened. The cup is concentric with respect to the core and is of substantially larger diameter as shown. The cup telescopingly receives the apertured cylindrical housing 24, which in turn mounts the closure cap 28. To maintain the core 19 suitably within the housing 24 there is employed a metal strip 30 which extends upwardly through a central opening 3| of the core I0 and engages with the diametric slots 32 thereof. The lower end 33 of strip 30 may be bent or riveted over the bottom of the insulation plate 25. A suitably slotted curved leaf spring 34 is slid over the opposite end of the strip 30 whereupon the cap 28 is placed thereon, and the upper extremity 35 of strip 30 is also turned or riveted over the end of said cap to complete the securement of the respective parts and to maintain the wound core fixedly but resiliently within the housing 24. Any suitable mounting means 36 may be spot welded, riveted, or otherwise secured to the housing 24 to afford means for fixing the complete unit of the chassis or other base plate of the machine or device with which the unit is used.

Thus, among others, the several objects of the invention as afore noted are achieved. Obviously numerous changes in construction and rearrangement of the parts might be resorted to without departing from the spirit of the invention as defined by the claims.

I claim:

1. A resistor, comprising a bored core of insulation material having axially extending slots spaced circumferentially about its outer wall and extending continuously from end to end of said core, said slots being of inverted T formation; electric terminal members disposed within said slots in frictional engagement with walls thereof, said members projecting from one end of said core; electrical resistance elements wound upon said core and connected with selected terminal members; a plate of insulation material disposed at the end of said core and receiving the terminal members projecting therefrom; cover supporting means carried on said plate; a cover disposed about said core in spaced relationship with the resistance windings thereon; a cap for said cover at the end opposite said plate; a tie member extending through the core bore and said plate and cap to secure said cap and said cover relative to said plate; and spring means disposed between said cap and said core to secure said core within said housing.

2. A resistor, comprising a bored core of insulation material having axially extending slots spaced circumferentially about its outer wall and extending continuously from end to end of said core, said slots being of inverted T formation; electric terminal members disposed within said slots in frictional engagement therewith, said members projecting from one end of said core; electrical resistance elements Wound upon said core and connected with selected terminal members; a plate of insulation material disposed at the end of said core and receiving the terminal members projecting therefrom; an enclosure for said core, said enclosure being in spaced relationship with respect to the windings; a cover, means for securing said cover upon said enclosure, said means extending through the core bore, said cover and said plate; and means disposed within said cover intermediate the end thereof and an end of said core to secure said core against movement within said enclosure.

3. An electrical resistor, comprising a core member having slots disposed in spaced relationship about the circumference of the core, said slots extending to at least one end of the core and. having a narrow entrance passage communicating with a relatively wide channel; terminal members disposed within said slots, said members each comprising a strip member bowed to frictionally engage a wall of said channel and a connection head extending outwardly therefrom, said head being Wider than the entrance passage of said slot, and having a neck portion of less width than the entrance passage; and resistance elements wound upon said core and connected to selected terminal heads.

4. An electrical resistor, comprising a core member having slots disposed in spaced relationship about the circumference of the core, said slots extending to at least one end of the core and having a narrow entrance passage communicating with a relatively wide channel; terminal members disposed within said slots, said members each comprising a strip member bowed to frictionally engage a wall of said channel and a connection head extending outwardly therefrom, said head being Wider than the entrance passage of said slot; and resistance elements wound upon said core and connected to selected terminal heads.

5. An electrical resistor as in claim 4, in which certain of the connection heads comprise spaced branches respectively for the attachment of end portions of adjacent resistance elements thereto.

GEORGE J. MUCHER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,525,831 Steiner et a1. Feb. 10, 1925 1,809,089 Wiegand June 19, 1931 2,008,288 Malone July 16, 1935 2,035,911 Mucher Mar. 31, 1936 2,332,255 Podolsky Oct. 19, 1943 2,454,986 Beckman Nov. 30, 1948 FOREIGN PATENTS Number Country Date 123,106 Great Britain Feb. 20, 1919 

